As a core for a high-frequency acceleration cavity used for an accelerator for accelerating charged particles, a core using an Fe-based nanocrystalline soft magnetic alloy ribbon has been employed for its higher saturation flux density as compared with ferrite and also low loss (Patent Document 1).
Patent Document 2 describes a core for a high-frequency acceleration cavity using an Fe-based nanocrystalline soft magnetic alloy ribbon with a gap formed therein.
As an Fe-based nanocrystalline alloy ribbon for forming the above core, for example, the above Patent Document 2 discloses an alloy ribbon having a thickness of 10 to 30 μm (claim 3). Meanwhile, in terms of productivity, an Fe-based nanocrystalline soft magnetic alloy ribbon is typically cast to a thickness of more than 15 μm and used.
However, for a core for a high-frequency acceleration cavity, further reduction of losses has been required. As a method for reducing the eddy current loss, which is one of the losses in a core, generally, reduction of the thickness of an alloy ribbon is known.
Patent Document 3 describes a reforming method for improving the magnetic characteristics, according to which the surface of an amorphous alloy is mechanically ground or chemically ground. Specifically, it is described that the roll non-contact surface is ground 1 μm or less, preferably 0.5 μm or less.
Incidentally, a core for a high-frequency acceleration cavity is produced by winding and laminating an amorphous alloy ribbon for an Fe-based nanocrystalline alloy, followed by a heat treatment at a temperature not lower than the crystallization temperature. At this time, it is necessary to ensure insulation between layers of the alloy ribbon. Therefore, usually, a silica powder or alumina powder is applied to one side of a continuously cast alloy ribbon and then dried to form an insulating film, thereby increasing the degree of insulation between layers of the alloy ribbon.